Perfluorochloroolefin primer composition, method of coating therewith and article produced thereby



Nov. 22, 1960 E. LONG 2,961,341

PERFLUOROCHLOROOLEFIN PRIMER COMPOSITION, METHOD OF comma THEREWITH ANDARTICLE PRODUCED THEREBY Filed April 15, 1958 0,0 caafzhgoerffuorac/v/omo/efih pea/men coba/f ox/dechlarofrifluoraeffiy/enepaj/mez r/hver jubsfmfe are anticipated.

United States Patent PERFLUOR'OCHLOROOLEFIN PRIMER COMPO- SITION, METHODOF COATING Tl-IEREWITH AND ARTICLE PRODUCED THEREBY Lamar E. Long,Doylestown, Pa., assignor to Minnesota Mining and Manufacturing Company,St. Paul, Minn., a corporation of Delaware Filed Apr. 15, 19 58, Ser. N0. 728,524

20 Claims. (Cl. 117-75) This invention relates toa primer coatingcomposition comprising a mixture of a perfluorochloroolefin polymer andcobalt oxide. In one aspect this invention relates to a primer coatingcomposition comprising a mixture of a polymer of aperfiuorochloroethylene and a cobalt oxide. In another aspect thisinvention relates to perfluorochloroolefin polymer compositions whichhave improved adhesive characteristics. In another aspect the inventionrelates to chemically resistant coatings. Another aspect of theinvention relates to chemically resistant laminates. Still anotheraspect of this invention relates to a method of preparing halogenatedthermoplastic compositions having good adhesive characteristics andchemical resistance.

The invention will further be understood by reference to theaccompanying drawing wherein the sole figure is illustrative of apreferred embodiment.

There is a widespread demand in industry for protective coatings whichwill withstand the effects of severe environmental conditions. Manyprotective coatings are currently available but these are useful onlywhere high temperature and highly corrosive materials are notencountered.

Recent industrial developments have made available at high molecularweight, perfiuorochloroolefin polymers. These perfluorochioroolefinpolymers, for example, polymers of chlorotrifiuo-roethylene, have aunique combination of physical and chemical characteristics which hasled to their use in a variety of applications. Physically, thesepolymers which are flexible at low temperatures possess high thermalstability and excellent electrical properties and are, therefore, widelyused as electrical insulation particularly in situations where hightemperatures are expected. Chemically, these polymers offer excellentresistance to highly corrosive chemicals, such as fuming nitric acid,solvents such as aniline, acetone, alkalies, such as sodium hydroxide,etc., and are therefore Widely used where corrosive environmentconditions Although the perfluorochloroolefin polymers as a group possesdesirable physical and chemical characteristics, such as, in addition tothose memtio-ned above, low permeability, zero moisture absorption, hightensile strength, etc., their adhesive characteristics are poor,particularly their adhesion to metal surfaces. Therefore, it has beennecessary to utilize various techniques in order to provide adhesion.For example, by one method, it is necessary to provide an adhesivecoating to the surface and a mixed coating containing a major amount ofthe adhesive and a minor amount of the pertluorochloroolefin polymerbefore the final coating of perfiuorochloroolefin polymer can beapplied.

The plastic perfluorochloroolefin polymers also have high abrasiveresistance, high impact strength, and extreme toughness.

Other methods include sand blasting or etching the surface, however,these techniques provide only a mechanical bonding of the polymer to thesurface of the substrate, and as a result, the polymeric coating doesnot have a lasting adherence.

According to this invention a primer coating composition containing aperfiuorochloroolefin polymer and a cobalt oxide is applied to asubstrate such as, for example, a metal substrate, and is fused andcured thereon at'a temperature of between about 350 F. and about 600-F.

The perfiuorochloroolefin polymers in the primer coating composition ofthe present invention are plastic or elastomeric perfiuorochloroolefinpolymers, the monomers of which contain between 2 and 4 carbon atoms'andat least one normally gaseous halogen atom (chlorine or fluorine) forevery two carbon atoms in the olefin monomer. The preferred polymers ofthe present invention are the polymers of perfluorochloroolefinscontaining'between 2 and 3 carbon atoms in theolefin monomer.

Examples of the preferred perfiuorochloroolefin polymers are thehomopolymers of chlorotrifluoroethylene,

and the copolymers of chlorotrifluoroethylene with hydrogen-containinghalogenated olefins such as vinylidene fluoride, vinyl fluoride,vinylidene chloride, triflnoroethylene, chlorofluoroethylene and1,1,3-tri'fluorobutadiene.

Most preferred of the above-mentionedpolymers is the plastic homopolymerof chlorotrifluoroethylene and the plastic copolymer ofchlorotrifluoroethylene and 'vinylidene fluoride, which copolymercontains not more than ZO mole percent of vinylidene fluoride,preferably less than 6 mole percent.

High molecular weight plastics or elastomers of the above-mentionedpolymers having molecular weight above 50,000 are those which arepreferably employed in this invention as distinct from low molecularweight polymers of the same monomers which exist in oil, grease and waxrange. In applications of putties and caulking fluids, these lowermolecular weight polymers may be employed. The high molecular weightpolymers referred to are normally solid and have softening points above150 C. and, in the case of the plastic homopolymers of chlorotrifluormethylene, have no strength temperatures (NST) of at least 220 C. andpreferably above 250 C. These high molecular weight polymers areemployed in the coating compositions and laminates of the presentinvention.

For the purpose of this invention the preferred copolym'er ofchlorotrifluoroethylene and vinylidene fluoride contains above about 80mole percent and below 100 mole percent chlorotrifiuoroethylene.Copolyme'rs con taining between and mole percent ofchlorotrifluoroethylene have resinous characteristics and are soluble ina number of common organic solvents. Copolymers be tween 20 and 69 molepercent of chlorotrifluoroethylene are elastomeric. The selection of theproper copolymer mole ratio depends on the ultimate use and desiredproperties of the blend. However, it has been found that for mostcoating compositions a chlorotrifluoroethylene and vinylidene fluoridecopolymer composition containing above 80rnol'e percentchlorotrifluoroethylene isdesirable.

In the process of this invention a dispersion of polymer particles in avolatile dispersing vehicle is preferably-cmployed wherein the particlesize of the polymer is generally that of a finely divided powder, thatis, at least percent through a number 12 sieve, preferably'anumber 200sieve in the US. Bureau of Standard Series. In the case of achlorotrifiuoroethylene polymer the particle size is most preferably notmore than 50 microns.

The primer coating compositions of this invention are generallyappliedby techniques which. employ a Evolatile dispersing vehicle whichpreferably wets the particle surfaces of the perfluorochloroolefinicpolymer and in which the polymer and cobalt oxide is insoluble. However,it is also within the scope of this invention, particularly where themore soluble elastomeric polymers are employed, to prepare a solution ofthe polymer wherein the cobalt oxide particles are suspended or toemploy the polymer-cobalt oxide mixture as a dry powder. Examples ofvolatile dispersing vehicles which may be suitably used in thisinvention are the aromatic hydrocarbons such as for example, benzene,toluene, xylene, etc.; aromatic and aliphatic ketones such as, forexample, methyl ethyl ketone, diisobutyl ketone, diphenyl ketone, etc.,aliphatic esters such as amyl acetate, ethyl acetate, ethyl propionate,and water, particularly when used in combination with any solublewetting agent such as, for example, acetone, butanol, pentanol, etc.

The cobalt oxide which is suitably blended with theperfiuorochloroolefinic polymer includes cobaltous oxide (C), cobalticoxide (C0 0 and cobalto-cobaltic oxide (C0 0 In certain instances, whereit is desirable to fuse the halogen-containing polymer at a highertemperature than is generally used, i.e., at a temperature of about 600F. or higher, a chromium oxide, a molybdenum oxide and/or a molybdenumsulfide may be added to the cobalt oxide primer to deter degradation ofthe polymer. Examples of such mixtures are the combination of molybdenumtrioxide with cobalt oxide, molybdenum sulfide with cobalt oxide,chromic oxide with cobalt oxide, and molybdenum trioxide and chromicoxide with cobalt oxide primer.

The cobalt oxide employed in this process is in a finely divided stateor a powder which will pass through a 100 mesh screen and which willpreferably pass through a 300 mesh screen in the US. Bureau of StandardSeries. The particles are preferably dispersed in a volatile organicvehicle or dispersant before or during the time of blending with theperfluorochloroolefin polymer and the more finely divided the particlesize of the oxide, the better the dispersion. Suitable dispersants arethe same as those recited above for the perfluorochloroolefin polymer.

In preparing the compositions of this invention, between about 5 partsand about 60 parts by weight, preferably between about 20 parts andabout 50 parts by weight of the cobalt oxide are blended with each 100parts by weight of perfluorochloroolefin polymer. The polymer to cobaltoxide ratios most preferably employed is between about 3:05 and about3:2. Generally, where maximum chemical resistance is required, thecobalt oxide constitutes a minor proportion of the composition, whereaswhere maximum bond strength is required, the cobalt oxide constitutes aproportion of the composition approaching 50 percent by weight or more.

The preferred primer coating compositions of the present inventioncomprising cobalt oxide and per'fiuorochloroolefin polymer are used ascoatings on various substrates. These coatings may be applied to metalsurfaces, for example, steel, Inconel, Monel, zinc, cadmium, magnesium,brass and aluminum surfaces, to asbestos surfaces, to concrete surfaces,to glass surfaces and to any plastic surface which will withstand hightemperatures, for example, temperatures up to about 600 F. withoutdegrading. Examples of such plastic surfaces are a polyurethan surfaceand a silicone plastic surface. The primer coating compositions can belaid down on the substrate as an initial coat which adheres to thesurface and to subsequent coatings of unblended polymer which form asurface coating on top of the initial coat. Examples of some of theapplications for this type of coating, are coatings for metal reactorsand laminates bonded to suitable fabrics such as glass cloth. The primercoating compositions of this invention, however, can also be applied toa substrate in a desired thickness and used as the sole surface coating.This application is illustrated by the use of chlorotrifiuoroethylenepolymer blended with cobalt oxide for use as a release coating on tiremolds, etc. In cases where the primer coating composition is the onlycoating applied to a substrate it is generally preferred to employ aperfiuorochloroolefin plastic in the primer composition. While thecobalt oxide when present in the final coating decreases the chemicalresistance of the coating, still the amount of perfluorochloroolefinplastic used may provide sufficient chemical resistance for the desiredapplication. For some uses such as release coatings, very littlechemical resistance may be required. Sometimes only a small amount ofcobalt oxide within the lower portion of the above range need beemployed in the primer coating composition to give the desiredadherence. This is very often the case when applying a coating to anatural or synthetic fabric where the coating permeates the intersticesof the woven fibers and is thus mechanically bonded to the fabric. Inthis instance such a small amount of cobalt oxide need be employed, thatits effect on the polymer in the primer coating composition is almostnegligible. In cases where the coating material will be exposed tostrong chemical action it is preferable to employ the primer coatingcomposition as the initial coat over which a compatible chemicallyresistant plastic coating is applied. When maximum chemical resistanceand bond strength is desired it is most preferred to employ a plasticperfluorochloroolefin polymer which is the same polymer in the primercoating composition as in the subsequent unblended polymeric coatingsapplied to the substrate. Particularly suitable for this purpose are theplastic polymers of chlorotrifluoroethylene.

Although dissimilar polymers may be employed if so desired, they must becompatible and it is generally preferred that the perfiuorochloroolefinpolymer in the primer coating composition contains the same amount orless fluorination than the unblended polymeric coatings to be appliedthereon.

Previous primer coatings have required that a mixed coa be applied priorto the application of a final coat. However, when using the blend of thepresent invention the final unblended coating can be applied directlyover the primer coat. This development represents an important chemicaland economic advantage over primers previously used. Additionaladvantages include the strong adhesion to the substrate and to theunblended plastic over-coat, the absence of delamination upon aging, theflexibility, high temperature stability and chemical resistance of theseprimers over most of those known and used heretofore.

To obtain a fine particle size of the cobalt oxide, the inorganiccompound can be dry milled or milled in a volatile vehicle for a periodof from 1 to 20 hours, more often for a period of from 2 to 5 hours oruntil the desired particle size is obtained. The milled oxide is thenadded to the perfiuorochloroolefin polymer dispersion to provide adispersion having a total solids concentration of between about 20 andabout percent total solids; preferably between about 30 and about 65percent total solids. Another method of reducing the particle size ofcobalt oxide comprises milling the oxide after it has been added to theperfluorochloroolefin polymer dispersion. In the case ofchlorotrifluoroethylene polymer the milled oxide can be added to any ofthe commercially available dispersions of that polymer which aredisclosed in US. Patent Nos. 2,775,569 and 2,686,767. Any suitablegrinding apparatus may be employed for this purpose, for example, a ballmill, a roller mill and a pebble mill.

In addition to the cobalt oxide and perfluorochloroolefin polymer, theprimer compositions of this invention can contain various additiveswhich are included to alter or improve some of the physicalcharacteristics. For example, plasticizers can be added. Suitableplasticizers include the low molecular weight perfluorochloroolefinpolymers, such as the polymers ofand telorners-ofchlorotrifluoroethylene. The low molecular weight homopolymer ofchlorotrifluoroethylene ranges from relatively mobile liquids to waxes.One of the preferred low molecular weight telomers' ofchlorotrifiuoroethylene is the homotelomer which has the general formulaC1( CF CFCD CI in which n varies from about 4 to about 20. Theseplasticizers are soluble in the volatile dispersing vehicle and whenused, they are added in an amount between about 1 and about 40 parts byweight per 100 parts by weight of the perfiuorochloroolefin polymer.Although the addition of plasticizers is preferred since it results inmore flexible coatings having smooth glossy surfaces, it is not anessential ingredient in the primer coating composition.

Chromic oxide maybe added to increase bonding strength of theprimer'base coat to a metal surface and is used only when extremely highbonding strengths are required. Other bonding aids which can be added tothe blend are potassium permanganate, molybdenum sulfide and apolyurethan prepared by the reaction between a polyisocyanate and apolyalcohol. Examples of suitable polyurethans employed for this purposeare reaction products of diphenylmethanediisocyanate andpolyethylfillers such as, for example, mica or bentone can also be addedto the primer composition, in which case they constitute from 0.1 to 20parts by weight per 100 parts by weight of polymer. The addition ofthese fillers aids in the application of primer to a substrate by themethod of dipping or slush coating, although the same effect can beaccomplished by increasing the solids content in the dispersion, such asby increasing the amount of cobalt oxide and/or polymer in thedispersion.

After the primer coating composition has been prepared and thoroughlymixed, it can be applied to a surface by using a spray, dip, knife orflow coating technique depending upon the viscosity of the dispersion,solution or slurry. After the primer composition has been applied to asubstrate by any of the above techniques, it is fused into a continuousadherent film by heating. Fusion temperatures range between about 350 F.and about 600 F., preferably between about 450 F. and about 560 F., forexample, 500 F. to 520 F., and are applied for a period of from about afew seconds to about 2 hours, preferably for a period not in excess ofabout 1 hour. In cases where the primer composition contains a plasticperfluorochloroolefin polymer and no plasticizer, the fusion is effectedby heating the primer composition at a temperature above the first ordertran sition temperature of the polymer which is about 220 C. in the caseof polychlorotrifluoroethylene. Generally,

2 The primer coating composition may also be applied to the surface as adry powder, without the use of a volatile dispersing vehicle.

the higher the fusion temperature, the shorter the residence period ofthe primer coating composition at that temperature. The residence periodis also determined by the method employed for heating. For example, thesubstrate may be placed in an oven and baked for a period of hours or itmay be flame sprayed at a very high temperature (about 600 C.) for a fewseconds. Subsequent applications of primer coat may be laid down in themanner stated above allowing each layer to air dry and fusing after eachapplication. When the primer coating composition is to be used as afinal coating, layers of the primer coating composition can be laid downup to thicknesses about 25 mils or higher, although coatings of morethan about 10 mils generally are not required. When the primer coatingcomposition is employed as an intermediate coating layer, thicknesses ofnot more than about 6 mils are employed, since at higher thicknessesthere is a tendency for the coating to mud crack.

In both of the above cases a minimum thickness of about 2 mils of theprimer coating composition is employed. The primer coating compositionmay be applied in a series of coating steps or it may be applied in asingle step. When used as a base coat or intermediate coat, the outerand final coatings of unblended polymer, i.e., polymer which contains nocobalt oxide is applied in thicknesses ranging between about 5 and about25 mils, and preferably between about 8 and about 12 mils.

In a preferred embodiment two applications of the primer coat, whereineach application amounts to about a 2 mil thickness, are laid down on asubstrate and fused and about 9 mils of outer coating is applied thereonand cured.

After the final coating of unblended plastic is applied to the surface,the coating is cured thereon at a temperature between about 350 F. andabout 600 F., preferably at a temperature between about 450 F. and about500 F. depending upon the amount of plasticizer present for a period offrom about 2 hours to about 25 hours, preferably for a period notexceeding 12 hours.

When fusing or curing the primer coating, the adhesion to a surface maybe enhanced by applying pressure to the coated surface. The applicationof pressures up to about 7,000 p.s.i.g. or higher are at timesparticularly useful when it is desirable to employ temperatures withinthe lower portions of the fusing and curing ranges set forth above. Whenpreparing a laminate the use of pressure ispreferred since the liquidprimer coating, which is forced into the interstices of the fabric,provides a better bond with the fabric.

The finished coating, which is prepared by any of the methods or by themodification of any of the methods set forth above, is strongly adherentto the substrate and cannot be 'pealed, chipped or cracked. The coatedportion can be aged in the presence of strong acids or alkalies, atelevated temperatures with no noticeable weakening of the adherentstrength. While I do not wish to be bound or limited by any particulartheory of operation, it is believed that the metal of the cobalt oxideforms a coordination compound with a halogen of the polymer thusproviding a chemical bond and that the metal of the cobalt oxide platesout on the substrate, promotes the growth of nodules and providesdendrite growth on the surface of the metal. This theory would accountfor the exceptional adhesive properties of the primer.

The following examples are offered as a better understanding of thepresent invention and are not to be construed as unnecessarily limitingthereto.

In each of the following examples where the primer coating compositionswere used on steel panels, the steel was degreased and grit blastedbefore the primer was applied. Detailed information on the preparationof the primer coatings and the application of the coatings is given inExamples 1, 2, 4 and 5. Similar techniques were used in each of theexamples reported in the table.

The above primer coat was prepared by mixing 2880 grams ofpolychlorotrifluoroethylene dispersion (40 percent by weight ofpolychlorotrifluoroethylene dispersed in a 50-50 mixture of xylene anddiisobuytl ketone) with 288 grams of cobalt oxide (73.5 percent cobalt)in a pebble mill. After milling for 4 hours, 432 grams of xylene wasadded to readjust the solids to 40 percent.

Two coatings of the above prepared primer coat were applied to steelpanels by spraying. After partial air drying, each coat was baked for 45minutes at 510 F. (substrate temperature). Six coats of commercial Kel-FNW-25-TR dispersion (a dispersion of polychlorotrifluoroethylene, NST310 C.) were applied over the primer coat by spraying. After partial airdrying, each of the intermediate coats was baked for 45 minutes at 500F. (substrate temperature) and the sixth coat was baked for five hoursand 45 minutes at 500 F. (substrate temperature) after which the panelwas quenched in water. The total primer thickness was 4 mils and thetotal thickness of polychlorotrifluoroethylene was mils as determinedwith a fihn thickness gauge.

A panel thus coated was subjected to steam, 240 F. and 10 p.s.i.g., for100 hours without loss of adhesion. Unprimed polychlorotrifluoroethylenecoatings lose adhesion to steel after one hour of similar steamtreatment. Another panel thus coated was heat aged in an oven at 300 F.for 100 hours without loss of adhesion.

acetate) with 360 grams of cobalt oxide (73.5 percent cobalt) in apebble mill for 4 hours. After milling, 360 grams of amyl acetate wasdecanted to adjust the solids to 40 percent.

A portion of the above dispersion was used to prepare a dip coatingprimer by decanting 202 grams of amyl acetate and adding 286 grams ofcopolymer solution (12.2 percent by weight of copolymer in amylacetate). This primer was thinned with amyl acetate to a Zahn G-2 cupviscosity of 30 seconds. Two coats of primer were then applied to a 0.25inch steel rod by immersing the rod in the primer, withdrawing slowlyand air drying and baking for 45 minutes at 510 F. (substratetemperature) between each coat. Four coats of commercial Kel-F N-2dispersion (a dispersion of polychlorotrifluoroethylene and copolymer ofchlorotrifluoroethylene and vinylidene fluoride in amyl acetate) werethen applied over the primer coating. The Kel-F N-Z dispersion wasthinned to a Zahn G-2 cup viscosity of 20 seconds and the rod was bakedfor 45 minutes at 500 F. (substrate temperature) after each immersionuntil the final coat, which was baked for 5.5 hours at 500 F. (substratetemperature), was applied.

The total primer coat thickness was 2.5 mils and the thickness of thetotal unprimed dispersion was 4 mils as measured with a micrometer. Thecoated steel rod was subjected to steam, 240 F. and 10 p.s.i.g., for 100hours without loss of adhesion.

Example 3 Two six-inch long, one-inch diameter glass reinforcedepoxytubes (constructed of glass cloth and Epon 828 resin cured withmetaphenylenediamine catalyst) were dip coated with the primer preparedin Example 2 followed by Kel-F N-2 dispersion also described in Example2. The tubes received two coats of primer thinned toa Zahn G-2 cupviscosity of seconds with amyl acetate. Each coat was baked 45 minutesat 510 F. (substrate temperature) before applying the next coat. Threecoats of Kel-F N-2 dispersion thinned to a Zahn G-2 viscosity of 20-26seconds with amyl acetate were then applied over the primer by dipcoating. The two intermediate coats of Kel-F N-2 dispersion were eachbaked for 45 minutes at 500 F. (substrate temperature) after applyingand the final coat was baked for four hours at 500 F. (substratetemperature). Upon completion of the final bake, the tubes were quenchedby immersion in water. It was impossible to strip the primed coatingfrom the tubes.

Similar tubes were dip coated without primer by applying five coats ofKcl-F N-Z dispersion thinned to a Zahn G-2 cup viscosity of 26 secondswith amyl acetate to the tubes. The first two coatings were baked for 45minutes at 510 F. (substrate temperature) after each application; coats3 and 4 were baked for 45 minutes at 500 F. (substrate temperature)after each application, and the final coat was baked for six hours at500 F. Upon completion of the final bake, the tubes were quenched byimmersion in water. The uuprimed Kel-F coating could be stripped veryeasily fiom the tubes.

The above primer was prepared by mixing 3240 grams ofpolychlorotrifluoroethylene dispersion (30 percent by weight ofpolychlorotrifluoroethylene dispersed in amyl acetate) and 486 grams ofcobalt oxide (73.5 percent cobait) in a pebble mill for 4 hours. Aftermilling, 81 grams of amyl acetate was decanted to adjust solids to 40percent and 2679 grams of this primer was used to prepare a dip coatingprimer. Amyl acetate (186 grams) was decanted and copolymer solution,286 grams 12.2 pgrlcednt by weight of copolymer in amyl acetate) was a eThe dip coating primer was thinned with amyl acetate to a Zahn G-2 cupviscosity of 32 seconds. Two coats of primer were applied to a 0.25 inchsteel rod by immersing the rod in the primer, withdrawing slowly and airdrying and baking for 45 minutes at 510 F. (substrate temperature) aftereach coat. Four coats of commercial Kel-F N-2 dispersion were thenapplied over the primer with baking for 45 minutes at 500 F. (substratetemperature) for each of the intermediate coats and baking for 5.5 hoursat 500 F. (substrate temperature) for the final coat. The commercialKel-F N-2 dispersion used above for coating had been thinned to a ZahnCir-2 cup viscosity of 20 seconds before it was applied by dip coating.

The total primer coating thickness was 3.0 mils and the total Kel-F N-2dispersion coating thickness was 3.0 mils as measured with a micrometer.The coated steel rod was subjected to steam, 240 F. and p.s.i.g., for100 hours without loss of adhesion.

A master batch of cobalt oxide was prepared by milling 2300 grams ofcobalt oxide (73.5 percent cobalt) and 1450 grams of volatile vehicle(50 percent xylene and 50 percent diisobutyl ketone) in a one gallonpebble mill for four hours. To a one gallon can was charged 475 grams ofthe cobalt oxide master batch prepared above and 2880 grams ofcommercial Kel-F NW-25-TR dispersion (a dispersion ofpolychlorotrifluoroethylene in xylene and diisobutyl ketone). Theingredients were mixed uniformly by shaking in a paint shaker for onehour.

Two coats of the above prepared primer were applied by spraying onto asteel panel with air drying and baking for 30 minutes at 540 F.(substrate temperature) between each application. Five coats ofcommercial Kel-F NW-ZS-TR dispersion (40 percent by weight ofpolychlorotrifluoroethylene dispersed in xylene and diisobutyl ketoneZahn G-l cup viscosity 32 to 34 seconds) were applied over the primercoating by spraying. Each of the intermediate coats was air dried andthen baked for 45 minutes at 540 F. (substrate temperature) beforeapplying the next coating. The final coat was baked for seven hours at540 F. Upon completion of the final bake the steel panel was quenched byimmersion in water. Four additional panels were similarly prepared.

One of the coated panels was subjected to steam, 240 F. and 10 p.s.i.g.,for 100 hours without loss of adhesion. Other coated panels weresubjected to 37 percent hydrochloric acid, 98 percent sulfuric acid, 85percent phosphoric acid and 50 percent sodium hydroxide for 504 hours at180 F. without loss of adhesion.

While the above examples illustrate the economy and superiority ofchemically resistant coatings while eliminating the necessity for amixed coat, it should be noted that mixed coats can be used if desired.

The following examples in Table I were carried out using an intermediatecoat as a means for introducing stabilizers into the coatingcompositions which were applied and fused to steel panels. In each casea clean steel panel was coated with primer containingpolychlorotrifluoroethylene (NST about 310 C.), cobalt oxide and 50 molpercent vinylidene fluoride-50 mol percent chlorotrifiuoroethylenecopolymer dispersed in xylene in the manner described in the precedingexamples above. The following intermediate coatings were prepared,applied and baked thereon before applying the final coating ofcommercial KelF NW-ZS-TR.

l 30 percent by weight of po1ychlorotrifluoroethylene; Brookfieldviscosity about 10,000 centipoises.

I Good adhesion of film. Film shows no evidence of degradation and hasgood flow properties.

Although the experiments of Examples 6, 7, 8 and 9 employ the techniquewhereby the stabilizer is introduced in an intermediate coat, equallysatisfactory results can be obtained by introducing the stabilizerdirectly into the primer coating composition before applying to thesubstrate.

The invention herein described relates to a primer coating compositioncomprising a polymer of a perfluorochloroolefin and a cobalt oxide, bothof which are preferably dispersed in a volatile liquid dispersionvehicle. The resulting composition is fused and cured on a substrate togive a strongly adhesive and chemically resistant coating thereon. Themethod for preparing the primer coating compositions of this inventionmay be of the methods or any various modifications and alternatives ofthe procedure herein described and may become apparent to those skilledin the art without departing from the scope of this invention.

Having thus described my invention I claim:

1. A primer coating composition consisting essentially of a volatileorganic dispersing vehicle, parts by weight of a solidchlorotrifluoroethylene polymer selected from the group consisting ofthe homopolymer thereof and the copolymer thereof with vinylidenefluoride and between about 5 parts by weight and about 60 parts byweight of a cobalt oxide.

2. The composition of claim 1 wherein the normally solidperfluorochloroolefin polymer is a plastic homopolymer ofchlorotrifluoroethylene.

3. The composition of claim 1 wherein the normally solidperfluorochloroolefin polymer is a copolymer of chlorotrifluoroethyleneand vinylidene fluoride.

4. The composition of claim 1 wherein the cobalt oxide is cobaltousoxide.

5. The composition of claim 1 wherein the cobalt oxide is cobalticoxide.

6. The composition of claim 1 wherein the cobalt oxide iscobalto-cobaltic oxide.

7. The composition of claim 1 wherein the volatile organic vehicle isamyl acetate.

8. .The composition of claim 1 wherein the volatile organic vehicle isxylene.

9. The composition of claim 1 wherein the volatile organic vehicle is amixture of diisobutyl ketone and xylene.

10. A primer coating composition consisting essentially of a volatileorganic dispersing vehicle, 100 parts by weight of a solidchlorotrifluoroethylene polymer selected from the group consisting ofthe homopolymer thereof and the copolymer thereof with vinylidenefluoride, between about 5 and about 60 parts by weight of a cobalt oxideand between about 0.1 and about 5 parts by weight of a polymerstabilizer.

11. The primer of claim 10 wherein the stabilizer is molybdenumtrioxide.

12. The primer of claim 10 wherein the stabilizer is chromic oxide. 1

from the group consisting ofthe homopolymer thereof" and the copolymerthereof with vinylidene fluoride having a molecular weight above50,000'and betweenabout parts by weight and 60 partsby Weight ofa-cobalt oxide dispersed in a volatile organic vehicle;

15. An article of manufacture which consists essentially of a substrateand a coating comprising afused mass of solid chlorotrifiuoroethylenepolymerselected 1 fromthe group consisting of the homopolymer thereofand the copolymer thereof with vinylidene fluoride-and -a cobalt oxide,said coating containing between-about-Sand-about- 60 parts by weight ofsaid cobalt oxide per 100 parts by weight of said polymer.

16. The article of claim 15 wherein the substrate ismetal.

17. An article of manufacture which consistsressentially of a substrate,and an intermediate.adhesive coating comprising a fused mass of .solid.chlorotrifluoroethylene; polymer selected from thegroup consisting ofthe-homo-' polymer thereof and the copolymer thereof .with.vinylidenefluoride and a cobalt oxide, said coating containing between about 5 andabout 60 parts by. weight of said cobalt oxide per 100 parts by weightof said polymer, and an outer protective coating comprising. a normallysolid:

polymer of a perfluorochloroolefin.

18. An article of manufacture which consists essentially of a metalsubstrate, an intermediate adhesive coating comprising a fused mass of100 parts by weight of a-solid high molecular weightchlorotrifluoroethylenepolymer selected from the group consisting of thehomopolymer thereof and the copolymer thereof with vinylidenefluoride,between about 1 and about 40 parts by weight of "a low molecular weightpolymer of chlorotrifluoroethylene and.

between about 5 parts by weight and about parts by weight of a cobaltoxide and an outer protective coating comprising a polymer ofchlorotrifluoroethylene.

19. A process'which comprises applying to a substrate a coatingcomposition consisting essentially of a volatile dispersing-vehicle, achlorotrifluoroethylene polymer selected from the group consisting ofthe homopolymer thereof and the copolymer thereof with vinylidenefluoride and a cobalt oxide, said composition containing between about 5and about 60 parts by weight of said cobalt oxide per parts by weight ofsaid polymer and heating said coating composition to a temperaturebetween about 350 F. and about 600 F. to provide a fused adherentcoating on the surface of the substrate.

20. A process comprising applying to a metal substrate a coatingcomposition consisting essentially of a volatile organic dispersingvehicle, a chlorotrifluoroethylene polymer selected from the groupconsisting of the homopolymer thereof and the copolymer thereof withvinylidene fluoride and a cobalt oxide, said composition containingbetween about 5 and about 60 parts by weight of said cobalt oxide per100 parts by weight of said polymer, heating said coating composition toa temperature between about 350" F. and about 600 F. to provide a fusedadherent coating surface of the substrate; applying thereon a coating ofa solid perfluorochloroolefin polymer having a molecular weight above50,000 and curing the entire coating at a temperature between about 350F. and about 600 F.

References Cited in the file of this patent UNITED STATES PATENTS2,421,652 Robinson et a1 June 3, 1947 2,567,162 Sanders Sept. 4, 19512,707,703 Dorst May 3, 1955

18. AN ARTICLE OF MANUFACTURE WHICH CONSISTS ESSENTIALLY OF A METALSUBTRATE, AN INTERMEDIATE ADHESIVE COATING COMPRISING A FUSED MASS OF100 PARTS BY WEIGHT OF A SOLID HIGH MOLECULAR WEIGHTCHLOROTRIFLUORETHYLENE POLYMER SELECTED FROM THE GROUP CONSISTING OF THETHE HOMOPOLYMER THEREOF AND THE COPOLYMER THEREOF WITH VINYIDENEFLOURIDE, BETWEEN ABOUT 1 AND ABOUT 40 PARTS BY WIEGHT OF A LOWMOLECULAR WEIGHT POLYMER OF CHLOROTRIFLUOROETHYLENE AND BETWEEN ABOUT 5PARTS BY WEIGHT AND ABOUT 60 PARTS BY WEIGHT OF A COBALT OXIDE AND ANOUTER PROTECTIBE COATING COMPRISING A POLYMER OFCHLOROTRIFLUOROETHYLENE.